Magnetic excitation and hole doping effects of Haldane system

Haldane体系的量子涨落被观测到之后，人们从理论和实验两个方面进行了大量的研究。在无磁隙霍尔丹体系中掺杂杂质可诱发反铁磁性。在掺杂杂质的霍尔丹体系中，反铁磁性和间隙霍尔丹态共存，产生磁性新态。我们尝试观察了载流子掺杂霍尔丹体系中的磁激发，注意了载流子（空穴）的依赖性。为了用中子散射实验观察其详细的物理性质，选择了可以获得大尺寸单晶的Nd_2BaNiO_5。在T_N以上，Nd_2BaNiO_5中的Haldane间隙表现出与纯Haldane体系Y_2BaNiO_5相似的行为。Haldane态与T_N以下的反铁磁态共存，是近年来在交错应用领域中公认的一种独特的Haldane隙量子自旋链模型。在掺（Nd, Ca）_2BaNiO_5的空穴中，我们清楚地观察到T_N以上的动力学不相称结构。不可通约性δ与空穴浓度不成正比。这对应于氧化铜超导体中空穴浓度与δ的关系。当空穴掺杂在T_N以下时，发现了一种新的无磁色散激发，尽管这种激发能高于目前预期的能量。为了观察这种磁激发，我们尝试使用具有更好能量分辨率的ESR技术。由于我们成功地生长出了（Nd， Y, Ca）_2BaNiO_5的大单晶，并且我们可以自由地控制磁性Nd离子的影响，我们将在不久的将来进行中子实验。

After the quantum fluctuations in Haldane system have been observed, a lot of research has been performed both from theoretical and experimental sides. Antiferromagnetism can be induced by impurity doping in the non-magnetic gapped Haldane system. In this impurity doped Haldane system, antiferromagnetism and gapped Haldane state coexist, resulting in the magnetic new state.We tried to observe the magnetic excitations in the carrier doped Haldane system, paying attention to the carrier (hole) dependence. In order to observe the detailed physical properties with neutron scattering experiments, Nd_2BaNiO_5 was chosen for which a large-sized single crystal can be available. The Haldane gap in Nd_2BaNiO_5 has shown the similar behavior to that of pure Haldane system Y_2BaNiO_5 above T_N. The Haldane state coexists with antiferromagnetic state below T_N, which was recently recognized as a unique model of Haldane gap quantum spin chain in a staggered applied field.We clearly observed the dynamical incommensurate structure above T_N in the hole doped (Nd, Ca)_2BaNiO_5. The incommensurability δ is not proportional to the hole concentration. This corresponds to the relationship between the hole concentration and δ in the copper oxide superconductor. A new magnetic dispersionless excitation was observed with hole doping below T_N, although this excitation energy is higher than the energy currently expected. In order to observe this magnetic excitation, we try to use the ESR technique having a better energy resolution. Since we succeeded in growing a large single crystal of (Nd, Y, Ca)_2BaNiO_5 for which we can control the influence of magnetic Nd ion freely, we will perform the neutron experiment in near future..